This invention relates to an internal-combustion engine and, more particularly, this invention relates to an Otto engine using fuel gas in a low-temperature liquefied state as a fuel. Said liquid may be at a temperature of, e.g., -100.degree.C.
The absolute power output and the specific fuel consumption of Otto engines are largely dependent upon the intake temperature of the combustion air. At as small a temperature difference as 50.degree.C the difference in output may already be about 50% and in efficiency about 5%. The power output can be augmented by achieving greater volumetric efficiencies or smaller specific air volumes with correspondingly lower specific compression efficiencies by cooling or precooling the combustion air (intake air) prior to combustion.
It has been contemplated to provide means for heating the low-temperature liquefied (cryogenic) or cold liquefied gas prior to combustion by using exhaust heat from the engine. However this just-mentioned arrangement is disadvantageous when compared with the present invention.
The present invention contemplates providing apparatus and a method for recovering energy spent for low-temperature liquefaction of the fuel gas. It is particularly contemplated by this invention to provide an engine which achieves recovery of energy used for low-temperature liquefaction of the fuel gas by cooling the combustion air prior to combustion by its use as a heat-emitting heat-exchanging medium for preheating and/or pre-evaporating the low-temperature liquefied fuel gas.
This just-mentioned precooling process permits especially ecomonical recovery to be achieved of the liquefaction energy in the fuel gas, for with stoichiometric combustion (excess air factor .lambda.=1) the combustion air or intake air can be cooled by about 43.degree.C, the power output will be enhaced by about 45% and the efficiency will be improved to about 6% when use is made of methane (CH.sub.4) as a fuel gas. The specific power output and efficiency improvement will depend on the total initial temperature different of the intake air and the gas.
The corresponding figures of intake air cooling, power output, and efficiency for hydrogen would be 74.degree.C, 80% and about 10% respectively. The engine of this invention accordingly provides notable improvements in output and efficiency. The inventive process may also be termed cryogenic supercharging of an internal-combustion or Otto engine.
The cooling of the combustion air by preheating and/or pre-evaporating the liquid according to preferred embodiments of the invention can be achieved by indirect heat transfer in a suitable heat exchanger or by direct heat transfer resulting from the mixing of the combustion air with the liquid. For carburetor engines, the direct heat transfer embodiment is preferred.